Removal of ferrous sulfide deposits



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United States Patent 3,353,995 REMOVAL OF FERROUS SULFIDE DEPOSITS Fred Norman Teumac, Lake Jackson, Tex., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Mar. 26, 1964, Ser. No. 355,113 7 Claims. (Cl. 134-3) ABSTRACT OF THE DISCLOSURE This invention relates to an improved process for removing ferrous sulfide from ferrous metal surfaces by contacting such surfaces with a dilute (ll0%) aqueous solution of a strong mineral acid such as HCl or H 50 containing from about 0.1 to about 1.0 weight percent of copper ion and from 2 to 20 times the weight of such copper ions of a thiourea compound.

This invention relates to a method of removing ferrous sulfide deposits from ferrous metal surfaces, and more particularly to a method for removing such deposits with dr ic acid or sulfuric acid whereby the presence of free hydrogen sulfide is substantially minimized.

In many processes involving sulfur, deposits including ferrous sulfide (FeS) tend to build upon ferrous metal surfaces such as reactor walls, p ipipg, etc. Petroleum processing presents a particularly acute problem when sulfur is removed from the petroleum in a desulfurizer. Deposits of coke containing as much as 80 percent ferrous sulfide may accumulate. Since hydrochloric acid (HCl) and sulfuric acid (H 50 generally react with the ferrous sulfide to produce hydrogen sulfide (H 5) which is extremely toxic and generally very corrosive to ward materials commonly used in construction, sulfuric acid and hydrochloric acid, although readily available, economic materials, are seldom used to remove ferrous sulfide-containing deposits from such metal surfaces.

A common method of removing ferrous sulfide-containing deposits is to subject the deposit-supporting ferrous material to high temperatures in the presence of oxygen. Such methods are usually costly and are inherently dangerous to the ferrous material of construction.

I have discovered a method whereby unexpectedly, ferrous sulfide is safely removed from ferrous metal surfaces by means of dilute strong mineral acids without the presence of significant amounts of free hydrogen sulfide.

In accordance with the present invention, an aqueous solution. containing from about 1 to about percent by weight sulfuric Q1 hydrochloric agigl, a soluble ggpper salt, copper ion being present in an amount of from about 0.1 to about 1.0 percent by weight and an amount of a thiourea compound equivalent to thiourea in an amount of from about 2 to about times the weight of copper ion present is employed to treat a ferrous metal surface which is contaminated by a ferrous sulfide-containing deposit, thereby to react with the ferrous sulfide-containing deposit and safely remove said ferrous sulfide without the presence of substantially any free hydrogen sulfide.

Copper ion is usually introduced to the solution by dissolving a suitable copper salt therein. Suitable copper salts are those having anions which do not form interfering byproducts during treatment. Appropriate soluble copper salts for use in the present invention are: copper sulfate (CuSO cupric nitrate (Cu(NO cupric acetate (Cu(C I-l O- cupric chloride (CuCl and the like.

Appropriate thiourea compounds for use in the present invention are: thiourea, 1,3-dimethyl thiourea, 1,3-

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diethyl thiourea, allyl thiourea, ethylene thiourea, and 1,3-diisopropyl thiourea. For clarity in expressing suitable solution composition and concentrations, all such references made herein will be based on thiourea. Quantities of the substituted thiourea compounds, therefore, will be expressed as the thiourea equivalent. To illustrate, when 1,3-dimethyl thiourea, 1,3-diethyl thiourea, allyl thiourea, ethylene thiourea, or 1,3-diisopropyl thiourea are substituied for thiourea, such substitution should be made in approximately equimolar amounts based on the desired concentration of thiourea.

When hydrochloric acid is employed, it is generally present in concentrations of from about 1 to about 10 percent by weight, with concentrations of from about 2 to about 5 percent by weight being preferred. Concentration of copper ion, when hydrochloric acid is employed, is generally from about 0.2 to about 1.0 percent by weight, with copper ion concentrations of from about 0.5 to about 1.0 percent by weight being preferred. Thiourea, when hydrochloric acid is employed, is generally present in an amount of from about 2 to about 10 times the weight of copper ion present, and preferably in a concentration of from about 2 to about 5 times the weight of copper ion.

When sulfuric acid is employed, it is generally present in concentrations of from about 1 to about 5 percent by weight, with concentrations of from about 3 to about 5 percent by weight being preferred. Copper ion, when sulfuric acid is employed, is generally present in an amount of from about 0.1 to about 0.5 percent by weight, with concentrations of from about 0.2 to about 0.5 percent by weight being preferred. Thiourea, when sulfuric acid is employed, is generally present in an amount of from about 10 to about 20 times the weight of copper ion present, and preferably from about 10 to about 16 times the weight of copper present.

Generally, treatment is carried out by contacting the surface to be treated with solution at ambient temperatures, although the solution may be warmed to facilitate dissolution of ferrous sulfide, if desired. Extreme high temperatures, i.e., near the boiling point of the solution, however, should be avoided since the presence of free hydrogen sulfide is more likely during such high temperature treatments, and the likelihood of copper plating of the ferrous metal surface is also increased.

Where operating conditions permit, the treatment is advantageously carried out under pressure in excess of atmospheric. Pressure is not, however, required for operability of the present invention.

A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, and are not to be construed to limit, the present invention.

Example 1 Furthermore, the expected precipitate of Cu S or Cus did not form.

Example 2 An aqueous solution was prepared containing 5 percent by weight HCl, 0.5 percent by weight of copper ion, and 2 percent by weight of thiourea. To the solution at ambient temperature was added a known amount of FeS. Substantially the same results were obtained as described hereinbefore in Example 1.

Example 3 In substantially the same manner as described in Examples 1 and 2, allyl thiourea, 1,3-dimethyl thiourea, 1,3- diethyl thiourea, ethylene thiourea, and 1,3-diisopropyl thiourea may be substituted, on an equimolar basis, for the thiourea employed therein, with substantially the same results.

Example 4 An aqueous solution containing 5 percent by weight sulfuric acid, copper sulfate in an amount equivalent to 0.4 percent by weight copper ion, and 9.6 weight percent allyl thiourea (equivalent to 6.3 weight percent thiourea). FeS added to the solution dissolved with no noticeable amounts of free H 8 being given off and no precipitate formed.

Example 5 t/ In substantially the same manner as described in Example 4, thiourea, 1,3-dimethyl thiourea, 1,3-diethyl thiourea, ethylene thiourea, and 1,3-diisopropyl thiourea may be substituted, on equimolar basis, for the allyl thiourea employed therein, with substantially the jame results.

Example 6 An aqueous solution containing about five percent by weight hydrochloric acid, about 0.5 percent by weight copper ions, and about 4 percent by weight thiourea was employed to remove ferrous sulfide from the interior surface of a ferrous metal pipe employed in a petroleum process. Removal of ferrous sulfide was readily accomplished by simple contact of the solution with the ferrous sulfide deposit the pipe. Substantially no free hydrogen sulfide was given off.

Substantially the same results were obtained when ferrous sulfide deposits were removed from petroleum process mby contacting the deposits with an aqueous soluacid, about 0.4 percent by weight copper ion, and about 6 percent by weight thiourea.

Various modifications may be made in the present invention without departing from the spirit or scope thereof, and it is to be understood that I limit myself only as defined in the appended claims.

I claim:

1. A method of removing ferrous sulfide from ferrous metal surfaces comprising providing an aqueous solution containing from about one to about ten percent by weight of an acid selected from the group consisting of hydrochloric and sulfuric acids, from about 0.1 to about 1.0 percent by weight of copper ion, and a thiourea compound selected from the group consisting of thiourea, 1,3- dimethyl thiourea, 1,3-diethyl thiourea, allyl thiourea, ethylene thiourea, and 1,3-diisopropyl thiourea, said thiourea compound being present in an amount equivalent to an amount of thiourea from about 2 to about 20 times the weight of copper ion present, and contacting the ferrous sulfide-containing ferrous metal surface with said aqueous solution, thereby to remove ferrous sulfide.

2. A method of removing ferrous sulfide from ferrous metal surfaces comprising providing an aqueous solution containing from about one to about ten percent by weight of hydrochloric acid, from about 0.2 to about 1.0 percent tron containing about five percent by weight sulfuric V by weight of copper ion, and a thiourea compound selected from the group consisting of thiourea, 1,3-dimethy1 thiourea, 1,3-diethyl thiourea, allyl thiourea, ethylene thiourea, and 1,3-diisopropyl thiourea, said thiourea compound being present in an amount equivalent to an amount of thiourea from about 2 to about 10 times the weight of copper ion present, and contacting the ferrous sulfide-containing ferrous metal surface with said aqueous solution, thereby to remove ferrous sulfide.

3. A method of removing ferrous sulfide from ferrous metal surfaces comprising providing an aqueous solution containing from about one to about five percent by weight sulfuric acid, from about 0.1 to about 0.5 percent by weight of copper ion, and a thiourea compound selected from the group consisting of thiourea, 1,3-dimethyl thiourea, 1,3-diethyl thiourea, allyl thiourea, ethylene thiourea, and 1,3-diisopropyl thiourea, said thiourea compound being present in an amount equivalent to an amount of thiourea from about 10 to about 20 times the weight of copper ion present, and contacting the ferrous sulfide-containing ferrous metal surface with said aqueous solution, thereby to remove ferrous sulfide.

4. A method of removing ferrous sulfide from ferrous metal surfaces comprising providing an aqueous solution containing about five percent by weight of hydrochloric acid, 0.5 percent by weight of copper ion, and about 2 percent by weight of thiourea, and contacting the ferrous sulfide-containing ferrous metal surface with said aqueous solution, thereby to remove ferrous sulfide.

5. A method of removing ferrous sulfide from ferrous metal surfaces comprising providing an aqueous solution containing about five percent by weight of hydrochloric acid, 0.5 percent by weight of copper ion, and about 4 percent by weight of thiourea, and contacting the ferrous sulfide-containing ferrous metal surface with said aqueous solution, thereby to remove ferrous sulfide.

6. A method of removing ferrous sulfide from ferrous metal surfaces comprising providing an aqueous solution containing about five percent by weight sulfuric acid, 0.4 percent by weight of copper ion, and about 9.6 percent by weight of allyl thiourea and contacting the ferrous sulfidecontaining ferrous metal surface with said aqueous solution, thereby to remove ferrous sulfide.

7. A method of removing ferrous sulfide from ferrous metal surfaces comprising providing an aqueous solution containing about five percent by weight sulfuric acid, 0.4 percent by weight of copper ion, and about 6 percent by weight of thiourea and contacting the ferrous sulfidecontaining ferrous metal surface with said aqueous solution, thereby to remove ferrous sulfide.

References Cited UNITED STATES PATENTS 2,049,517 8/1936 Saukaitis 134-4l 2,388,302 11/1945 Weyl 1343 XR 2,662,042 12/1953 Dougherty et a1 134-22 2,959,555 11/1960 Martin et a1. 134-3 XR JOSEPH SCOVRONEK, Primary Examiner. MORRIS O. WOLK, Examiner. I. ZATARGA, Assistant Examiner. 

1. A METHOD OF REMOVING FERROUS SULFIDE FROM FERROUS METAL SURFACES COMPRISING PROVIDING AN AQUEOUS SOLUTION CONTAINING FROM ABOUT ONE TO ABOUT TEN PERCENT BY WEIGHT OF AN ACID SELECTED FROM THE GROUP CONSISTING OF HYDROCHLORIC AND SULFURIC ACIDS, FROM ABOUT 0.1 TO ABOUT 1.0 PERCENT BY WEIGHT OF COPPER ION, AND A THIOUREA COMPOUND SELECTED FROM THE GROUP CONSISTING OF THIOUREA, 1,3DIMETHYL THIOUREA, 1,3-DIETHYL THIOUREA, ALLYL THIOUREA, ETHYLENE THIOUREA, AND 1,3-DIISOPROPYL THIOUREA, SAID THIOUREA COMPOUND BEING PRESENT IN AN AMOUNT EQUIVALENT TO AN AMOUNT OF THIOUREA FROM ABOUT 2 TO ABOUT 20 TIMES THE WEIGHT OF COPPER ION PRESENT, AND CONTACTING THE FERROUS SULFIDE-CONTAINING FERROUS METAL SURFACE WITH SAID AQUEOUS SOLUTION, THEREBY TO REMOVE FERROUS SULFIDE. 